Process of making hydrochloric and arsenic acids



PatentediMar. 6,

iii TAT CABLETON ELLIS AND VERNON T. STEWART, OF

MONTGLAIR, NEW JERSEY."

Ho Drawing. I

I To all whom it may coacemi Be it known that we, CARLEToN ELLIS andVERNON T. STEWART, citizens of the United.

hydrochloric acid on the other.

As a raw material for making the hydrochloric and arsenic acid, whitearsenic, (arsenic trioxid) preferably is employed and this may be eitherpure or may be of varying degrees of impurity as derived in commerce. Bythe treatment with chlorine, arsenic acid of afairly high degree ofpurity may be obtained. p y The chlorine employed for the purpose ispreferably obtained by brine and may purification and in fact chlorinwhen contaminated with a certain amount of moisture',.air or other gasesis suitable for carrying out the present process. I

referably arsenic trioxide or white arsenic is used as the raw material.This is made up into a suspension with water and a stream of chlorinegas or mixture of chlorine gas and air passed into the suspensionyielding arsenic acld' and hydrochloric acid. If the proportion of wateris largely in exeess'a dilute solution of arsenic'acid and hy'-drochloric acid is thus obtained. The. hydrochloric'acid may beseparated from the arsenicacid by boiling and suitably collecting theacid distillate. As this procedure involves the use of'a large bulk ofwater and consequent expense in concentration it is possible to use alesser proportion of water as for example only a sufficient amount ofwater to produce a paste or thin cream of the white arsenic and byagitating'such mixture to effectively react thereon with chlorine gasthus enabling hydrochloric acid to be readily removed from the place ofreacition and conveyed to suitable absorbing apparatus. In thisoperation the batch may be started coldbut preferably it is desirable toto a' process ofthe electrolysis 'oi be used without any especial thegases or vapors leaving the Application filed December 17, 1920. SerialIl'o. 431,348.

have the water slightly warm when the mixture is made up as the reactionstarts off more quickly. Depending-upon the conditions of treatment itmay be desirable also to continue the heating during the reactionor onthe other hand to cool the apparatus in case the reaction should becometoo violent and bring about entrainment of arsenic compounds. Water maybe introduced slowly into the batch during the reaction if the cream orpaste becomes too heavy through evaporation of water and its removal byhydrochloric acid.

The hydrochloric acid obtainedfrom this charge of material is sometimescontaminated with chlorine especially toward the end of the run. It alsomay contain entrained arsenic oxide or arsenic acid or arsenic chloride.Arsenic acid however is very rarely carried over by the HCl current, andthe oxidation of any white arsenic present in the hydrochloric acidaffords a means of re moval of the major portion at least of any'arsenic trioxid present in the gas or vapors.

Thus the gas may be passed through an oxidizing scrubber containingpermanganate or bic-hromate of soda in order to oxidize and retain sucharsenicalimpurity.

As stated, toward the close of the run (when the latch system is used) aconsiderable amount of'chlorine may be present in suspension of whitearsenic and to absorb the latter it is. desirable to passthehydrochloric acidgas and associated chlorine into a second absorbercontaining a fresh charge of white arsenic and water or into chambershaving shelves charged with ,white arsenic. Any impurity of chlorine inthe hydrochloric acid gas may be thus sufiiciently removed. The freshcharge of material used in this manner for the elimination of chlorinesubsequently forms the. primary charge in the actual stage of treatment(main treatment) with fresh chilorine gas to produce the hydrochloricand arsenic acids desired. Thus two closed tanks preferably equippedwith stirrers may be arranged to operate in series, one being used forcarrying-on the reaction proper and the second one being used to absorbchlorine present in the hydrofor the fresh charge.

A modified procedure involving a large bulk of water may be used in somecases as for example by using enough water with the white arsenic toabsorb the hydrochloric acid and preferably make a fairly concentratedsolution of the latter. When the oxidation is complete the solutioncontaining the hydrochloric and arsenic acid is boiled and thehydrochlorioacid thus separated from the arsenic acid. 4

In one case 4:00 grams of a sample of white arsenic was suspended inliters of water (forming a suspension containing somewhat over 11% ofwhite arsenic, assuming the arsenic to besubstantially pure) and treatedwith chlorine. The chlorine. was allowed to react until the whitearsenic was completely oxidized and as a slight sediment formed thesolution was filtered. lit was then boiled and all the hydrochloric acidand water eX- pelled leaving a residue of dry arsenic acid. On furtherheating above 140 C. combined water was eliminated yielding a residueofarsenic pentoxide. From the above charge of white arsenic 435 grams. ofthe pentoXide were obtained. The hydrochloric acid yielded by theforegoing operation amounted to 28'? grams which would represent over'500 grams of commercial aqueoushydrochloric acid.

In this particular example, the proportions were such as to give asstarting material, a suspension of white arsenic in water containingabout 11.43% of the white arsenic which (assuming a fair state ofpurity) would correspond to not substantially less than 11%. 1

The same favorable results can still be produced if the percentage ofarsenicis varied more or less, and this example is intended to besaecifically included in certain of the appended claims, under theeXpres sion not substantially less than 11% of arsenic trioxid.

It is, of course, understood that the example is given for illustrativepurposes and not as defining the limits or scope of the invention. r

Whether or not the arsenic acid is prd duced by the concentrated batchsystem or by the dilute system it is usuallynecessary to filter afteroxidation has been completed and the acid solution may be passedthroughglass wool or asbestos to remove silica and other impurities.

The oxidation also may take place in a tower or series of towers asuspension of the white arsenic in water being allowed to flowdownthrough towers having baifles or filling material so arranged thatdeposits of white arsenic may not form and clog the passages. in thisway the chlorine may be very completely absorbed as the current of gasprogresses always into contact with fresh portions of the white arsenicsuspension until absorption of the chlorine is complete. v This methodalso has the advantage ofbeing continuous. The solution of arsenic acidand hydrochloric acid obtained at the bottom of the tower may passthrough a filter and then into a stripping tank where the hydrochloricacid is continuously removed and by this stripping operationconcentrated arsenic acid obtained. It is usually unnecessary to carrythe concentration of the arsenic acid to an absolutely dry product andin fact according to the present invention in one form at least it isde-, sired to produce arsenic acid containing 20 to 25% or thereaboutsof water. This yields a syrupy product with specific gravityapproximately 2.(). The foregoing stripping process may also be appliedto the batch system of oxidation.

While in the above procedure we have indicated that chlorine may beintroduced at the bottom of the tower in order to secure acounter-current effect, it is not necessary in all "cases to do this,the chlorine in some cases" being for example added at the topof thetower or at suitable points along the sides thereof so that the chlorinegas moves in a generally downward direction with the flow of the liquidmaterial while absorption is taking place.

In making arsenical compounds from arsenic acid (especially when thelatter is used onthe premises) it is not always necessary to remove thehydrochloric acid c pletely or substai'itially completely,- a small.amount of hydrochloric acid may be cut when making for example calciumsenate without doing any harm other than to require a somewhat greaterquantity of lime than would be required for the are licacid alone. Thecalcium arsenate so formed 'of course Wlll contain a little calciumchloride. Thus it Wlll be ev1dent" that cording to circumstances it maybe more economical not to divest the arsenic acid completely of itshydrochloric acid. The cost of complete stripping may be such as torender the use of a product containing some hydrochloric acid cheaperand equally advantageous vunder some conditions.

To review therefore the foregoing process it comprises in its essentialfeatures a method of reducing chlorine to hydrochloric 3 acid and ofsimultaneously oxidizing a compound of arsenic preferably white arsenicto yield arsenic acid and in separating or stripping to a greater orless degree the arsenic acid from the hydrochloric acid and in. suitablypurifying or concentrating either or both of these products. I I

In order to get complete reaction between white arsenic or orescontaining white arsenic with chlorine it is not desirable to finish thereaction with the solution hot. Better results are obtained by havingthe solution cold or ifhot to cool it toward the end of the oxidationthereby securing compermissible to have arsenic in .a lower stage ofoxidation present.

'But in making insecticides in accordance with the preferred procedureof the present invention it is highly important and in fact essential torid the arsenic acid of arsenic trioxide. example by cooling thesolution such complete reaction is satisfactorily established.

What we claim is:

1. A process of making arsenic acid which comprises causing a stream ofa suspension containing arsenic trioxid to flow in contact with a gascontaining free chlorin, the said suspension containing initially notsubstantially less than 11% of arsenic trioxid.

2. A process of making arsenic acid which comprises causing a stream ofa suspension containing arsenic trioxid to flowin countercurrent contactwith a gas containing free chlorin, the said suspension containinginitially not substantiallyless than 11% of arsenic trioxid. i

3. -A process of making arsenic acid which comprises causing a stream ofa warm sus-- trioxid to flow in contact with a gas contaimng freechlorm,

pension containing arsenic the said suspension containing initially notsubstantially less than 11% of arsenic trio'xid.

4, A process of making arsenic acid which comprises causing a stream ofa suspension rontaining arsenic trioxid to flow in contact with a gascontaining free chlorm, the said For containing gas suspensioncontaining only-such an amount of water as to leave a syrupy product.

5. The process of making hydrochloric and arsenic acids which comprisesallowing,

an aqueous suspension containing white arsenlc to flow downwardly 1ncontact wlth a counter current of chlorin gas whereby arsenic acid andhydrochloric acid are produced and causing the arsenic acid togetherwith aqueous hydrochloric acid to pass through a hot zone whereby thearsenic acid is stripped in large part at least of the hydrochloricacid.

6. The rocess' of making hydrochloric and arsenlc acids which comprisesallowing a stream of an aqueous suspension con taining white arsenic toflow downwardly in contact with a counter current of chlorinewherebyarsenic acid and hydrochloric acid are produced,.and in cansing thearsenic acid together with aqueous hydrochloric acid to pass through ahot zone whereby the arsenic acid is stripped of a large proportion ofthe hydrochloric acid.

7. The process and arsenic acids a stream consisting of an aqueoussuspension of a lower arsenic oxide to flow downwardly in contact with acounter current ofchlorine gas, the liquid such contact, whereby arsenicand hydrochloric acids are produced, and causing the large part atleast, of hydrochloric acid.

CARLETON ELLIS. I v. T. STEWART.

of making hydrochloricwhich comprises allowing being hot during a partof arsenic acid together with aqueous hydro-

